Optical information recording and reproducing apparatus and optical information recording apparatus

ABSTRACT

An optical information recording and reproducing apparatus for recording information on a recording medium by forming interference fringes generated by interference between an information beam and a reference beam on the recording medium, and reproducing the information by irradiating the recording medium with the reference beam, in which the interference fringes are formed. The apparatus includes a spatial light modulator for spatially modulating at least a portion of the light beam emitted from a light source into the information beam, a light sensing device that reads the information beam extracted from the recording medium by the reference beam irradiated on the recording medium, a shift amount detector that detects a shift of an irradiating position of the light beam entering the spatial light modulator, and a device that corrects a positional shift between a position of an area for modulating the information beam and a position of the light beam in the spatial light modulator, based on a positional shift amount detected by the shift amount detector.

This application claims the benefit of Japanese Patent Application No.2005-344379, filed Nov. 29, 2005, which is hereby incorporated byreference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical information recording andreproducing apparatus, and an optical information recording apparatus,using a hologram capable of recording information with a higher densityand a larger capacity by recording optical interference fringes on arecording medium.

2. Description of the Related Art

These days, the world has entered an age of multimedia, and thenecessity for a recording apparatus that performs recording on arecording medium and a recording and reproducing apparatus that performsrecording and reproducing onto and from a recording medium has increasedin the level of importance, and the recording density has been raisedyear by year. In an optical information recording medium, also, progresshas been made from a CD (compact disk) through a DVD (Digital versatiledisk) to a BlueRay (Blue ray) disk. Responding to the progress made inthe optical information recording media, in the optical informationrecording apparatus, and the optical information recording andreproducing apparatus, also using the disk, the recording density hasbeen raised by shortening the wavelength of the light to be used. Inrecent years, a new recording system referred to as a holographic memoryhas been proposed. The holographic memory performs the recording ofinformation by forming a hologram corresponding to the information to berecorded inside the recording medium. Because of the characteristicsusing the hologram, a multiplex recording is made possible, and, even ifadjacent holograms have an overlapped portion with each other,information can be reproduced independently from these holograms.Consequently, the holographic memory can achieve a higher recordingdensity, which has not been obtainable in the conventional opticalinformation recording medium.

On the holographic memory, for example, a description is made inHideyoshi HORIGOME, et al., [Holographic medium near at taking off theground, 200 Gbyte expected to be realized in 2006], Nikkei Electronics,Vol. No. 891, pages 105 to 114, Jan. 17, 2005. In this article, therecording and reproducing apparatus by holographic memory using atwo-dimensional spatial light modulator and a light sensing device isdisclosed. Also, in this article, a description is made of an opticalsystem of the holographic memory system (optical information recordingand reproducing apparatus) of a coaxial type, referred to as a collinearsystem.

In the final analysis, in this optical information recording andreproducing apparatus, the information to be recorded is developed intosecond-dimensional digital pattern information, and by thissecond-dimensional optical pattern information, an information beam ismodulated. By this processing, the information beam is generated, inwhich the recording information becomes two-dimensional spatial beamintensity distribution image information. By allowing the informationbeam and the reference beam to interfere, the interference fringes arerecorded on the recording medium. At the reproducing time,two-dimensional digital pattern information is extracted and decodedfrom the beam intensity distribution image information reproduced byirradiating the reference beam. By this digital processing, it ispossible to inhibit the lowering of the reproducing error rate due todeterioration of an S/N ratio, and moreover, by coding binarized dataand performing error correction, it is possible to reproduce therecording information highly faithfully.

In the holographic memory system of the above-described collinearsystem, since the information beam and the reference beam have a coaxialoptical arrangement having no angle, recording and reproducing can beperformed by using one piece of an object lens. Hence, as compared to atwo-axis two light beam interference system allowing the informationbeam and the reference beam to irradiate the recording medium from adifferent optical path, there is the advantage that the optical systembecomes simple. Further, because of the configuration of the recordingmedium having a reflection film, there is the advantage that the opticalsystem can be arranged at one surface side of the disk-shaped recordingmedium.

SUMMARY OF THE INVENTION

Now, in the above-described conventional optical information recordingand reproducing apparatus, due to shape distortion, and the like, bytemperatures of members such as a light source, a lens, a beam splitter,and the like, there is often a shift that occurs in the positionalrelationship between the two-dimensional spatial light modulator and thelight beam incident on the spatial light modulator from a laser lightsource. Further, in the optical information recording and reproducingapparatus of this type, while it is assumed that the laser light sourceis exchanged, even due to insufficient reproducibility of the physicalposition at the time of such an exchange of the light source, a shiftmay occur in the positional relationship between the spatial lightmodulator and the light beam. When such a shift occurs, an adequate beamquantity necessary to form the interference fringes is not assured, anda portion of the interference fringes original to be formed is lost, inthe event that the interference fringes (volume hologram) is formed inthe recording medium by the reference beam and the information beam. Asa result, an erroneous hologram pattern is recorded in the recordingmedium, and, when the information is reproduced from the recordingmedium, an erroneous reproduced light beam is detected. An erroneousdetection of the reproduced light beam directly leads to the generationof a reproducing error.

Hence, an object of the present invention is to provide an opticalinformation recording and reproducing apparatus capable of correcting ashift or compensating for the shift, even when the shift occurs in thepositional relationship between the light beam incident on the spatiallight modulator and the spatial light modulator.

The optical information recording and reproducing apparatus of thepresent invention records information on a recording medium by forminginterference fringes generated by interference between an informationbeam and a reference beam on the recording medium, and, at the sametime, performs the reproducing of the information by irradiating thereference beam on the recording medium formed with the interferencefringes, and comprises a spatial light modulator for spatiallymodulating at least a portion of the light beam emitted from a lightsource and making it into the information beam, a light sensing devicethat reads an information beam extracted from the recording medium bythe reference beam irradiated on the recording medium, a shift amountdetector that detects a shift of the irradiating position of the lightbeam entering the spatial light modulator, and means that corrects apositional shift between a position of the information beam modulatingarea and the light beam in the spatial light modulator, based on thepositional shift amount detected by the shift amount detector.

The optical information recording apparatus of the present inventionrecords the information in the recording medium by forming interferencefringes generated by the interference between the information beam andthe reference beam on the recording medium, and comprises a spatiallight modulator for spatially modulating at least a portion of the lightbeam emitted from the light source and making it into the informationbeam, an optical system for allowing the reference beam and theinformation beam to interfere at a predetermined depth of the recordingmedium, and a shift amount detector that detects a shift of theirradiating position of the light beam incident on the spatial lightmodulator based on the positional shift amount detected by the shiftamount detector.

In the present invention, correcting means, for example, corrects thedetected positional shift amount by feedback. Further, as the spatiallight modulator, it is preferable to use a modulator having a pluralityof pixels and a configuration capable of allowing the effective pixel tofunction as a pixel for a reference beam and a pixel for an informationbeam. When such a spatial light modulator is used, the area of theeffective pixel of the spatial light modulator is divided into the areafor the reference beam and the area for the information beam, accordingto the position based on the detected positional shift amount, so thatthe correction of the positional shift can be performed.

As a specific configuration for correcting the positional shift, thereis such a configuration cited in which, when a shift register to write asignal is provided for each pixel in the effective pixel area, a startposition in the shift register is corrected, so that the positionalshift is corrected, or a configuration provided with means to allow aposition of the spatial light modulator to mechanically move toward theincident beam.

In the present invention, it is preferable to use a modulator/lightsensing device, in which the spatial light modulator and the lightsensing device are integrally formed on the same substrate. In such amodulator/light sensing device, as the positional relationship betweenthe spatial light modulator and the light sensing device, there arethose which arrange the spatial light modulator and the light sensingdevice on the substrate in a longitudinal direction and in a horizontaldirection. In the case of arranging in the longitudinal direction, thespatial light modulator and the light sensing device are laminated, suchthat the spatial light modulator is arranged at the light source side,and a pixel pitch in the spatial light modulator and a pixel pitch inthe light sensing device are matched, so that the pixel in the spatiallight modulator and the corresponding pixel in the light sensing deviceare arranged along an optical axis of the light incident from the lightsource, and at least a portion of the light incident on the spatiallight modulator transmits toward the light sensing device. In contrastto this, in the case of arranging in the horizontal direction, thespatial light modulator and the light sensing device are mutuallyarranged close to each other, so that the pixel in the spatial lightmodulator and the corresponding pixel in the light sensing device arenot overlapped along the optical axis of the light incident from thelight source.

In the present invention, as the spatial light modulator, it ispreferable to use a modulator having a plurality of modulators, in whichintensity of the reflection beam changes according to a modulatingsignal. Such a modulator is an element comprising, for example, areflection electrode to reflect the light from the light source and asemi-transparent film arranged on the light source side to thereflection electrode via a space, and showing a semi-transparency forthe light from the light source, wherein the reflectance of the lightfrom the light source changes through the control of a gap between thereflection electrode and the semi-transparent film. Alternatively, themodulator is a reflection type liquid crystal element.

That is, the present invention moves a position of the area modulated asthe information beam and the reference beam in the spatial lightmodulator in conformity to the light beam irradiated on the spatiallight modulator. As a result, the generation of a recording error and areproducing error due to a shift of the light beam from the light sourcecan be inhibited.

According to the present invention, even when the optical axis of theincident light is shifted or fluctuated for the spatial light modulator,a shift amount is detected by the element detecting such a shift andfluctuation, and can be corrected according to the detection positionalshift amount, and therefore, a relative positional relationship betweenthe incident light in the spatial light modulator and the display areaof the modulating signal can be always maintained similarly, as theinitial setting.

In the optical information recording and reproducing apparatus of thepresent invention, in order to detect a shift amount of the light beam,the element configured by semiconductor chips is increased by one justby the shift amount detector typically configured as an image sensor.However, it is also possible to use the light sensing device forhologram reproduction as a shift amount detector, and, in that case, ascompared to the conventional element, the number of semiconductor chipsdoes not increase. Particularly, by integrally providing the spatiallight modulator and the light sensing device on the same substrate, thenumber of such semiconductor chips can be reduced to one piece from twopieces. Since the spatial light modulator and the light sensing device,such as a CMOS sensor, are almost the same in each step of thesemiconductor process for manufacture these elements, there is noincrease in the number of steps, and it is possible to incorporate thefunctions of these elements all at once. As a result, despite the factthat the functions of correcting the positional shift of the light beamis added, the optical system is made much simpler as the opticalinformation recording and reproducing apparatus, thereby making itpossible to make a setting space much smaller. Further, since the writeto the recording medium and the read from the recording medium can beperformed approximately on the same axis, the positional shift betweenthe optical system for the write and the optical system for the read issubstantially eliminated, so that no adjustment of the optical shiftbetween both systems is required.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments, with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B and 1C are views showing the relationship between theposition of an incident beam on a spatial light modulator and amodulation information display position.

FIGS. 2A, 2B and 2C are views showing the relationship between theincident beam position on the spatial light modulator and the modulationinformation display position when the incident beam is shifted.

FIGS. 3A, 3B and 3C are views showing the relationship between theincident beam position on the spatial light modulator and the modulationinformation display position after the correction of the modulationinformation display position is performed.

FIG. 4 is a view for explaining an optical system of the opticalinformation recording and reproducing apparatus of a first embodiment ofthe present invention, and is a view showing from a light source to amodulator/light sensing device at the recording time.

FIG. 5 is a view for explaining another example of the optical system ofthe optical information recording and reproducing apparatus of the firstembodiment, and is a view showing from the light source to themodulator/light sensing device at the recording time.

FIG. 6 is a view for explaining the optical system of the opticalinformation recording and reproducing apparatus of the first embodiment,and is a view showing from the modulator/light sensing device to therecording medium at the recording time.

FIG. 7 is a view for explaining the optical system of the opticalinformation recording and reproducing apparatus of the first embodiment,and is a view showing from the light source to the modulator/lightsensing devices at the reproducing time.

FIG. 8 is a view for explaining another example of the optical system ofthe optical information recording and reproducing apparatus of the firstembodiment, and is a view showing from the light source to themodulator/light sensing device at the reproducing time.

FIG. 9 is a view for explaining another example of the optical system ofthe optical information recording and reproducing apparatus of the firstembodiment, and is a view showing light received from themodulator/light sensing devices through the recording medium at thereproducing time.

FIG. 10 is a view for explaining the optical system at the recordingtime in still another example of the first embodiment.

FIG. 11 is a view showing the arrangement of pixels in the shift amountdetector.

FIGS. 12A and 12B are views for explaining the measurement of the shiftof the optical axis of an incident beam.

FIG. 13 is a view showing the arrangement of pixels in the shift amountdetector.

FIG. 14 is a view for explaining an incident beam on the modulator/lightsensing device after correcting the shift.

FIG. 15 is an equivalent circuit diagram of the spatial light modulator,and is a view for explaining shift correction.

FIG. 16 is an equivalent circuit diagram of the modulator/light sensingdevice including a drive circuit portion.

FIG. 17 is a cross-sectional view showing the modulator/light sensingdevice configured by laminating the spatial light modulator and thelight sensing device using a reflection type light interferencemodulator in a longitudinal arrangement.

FIG. 18 is a graph showing a wavelength-reflectance characteristic ofthe modulator/light sensing device shown in FIG. 17.

FIG. 19 is a graph showing a wavelength-transmittance characteristic ofthe modulator/light sensing device shown in FIG. 17.

FIG. 20 is a view for explaining the shift correction in a secondembodiment of the present invention.

FIG. 21 is a cross-sectional view showing the modulator/light sensingdevice configured by arranging the spatial light modulator and the lightsensing device using the reflection type light interference modulator ina horizontal arrangement.

FIG. 22 is a graph showing a wavelength-reflectance characteristic ofthe modulator/light sensing device shown in FIG. 21.

FIG. 23 is a cross-sectional view showing the modulator/light sensingdevice configured by laminating the spatial light modulator and thelight sensing device using a reflection type liquid crystal on siliconin a longitudinal arrangement.

FIG. 24 is a cross-sectional view showing the modulator/light sensingdevice configured by arranging the spatial light modulator and the lightsensing device using the reflection type liquid crystal on silicon in ahorizontal direction.

FIG. 25 is a view showing the outline of a conventional opticalinformation recording and reproducing apparatus using a holographicmemory.

DESCRIPTION OF THE EMBODIMENTS

Next, preferred embodiments of the present invention will be describedwith reference to the drawings.

First, by referring to FIG. 25, a recording and reproducing apparatus bya holographic memory using a two-dimensional spatial light modulator(SLM) and a light sensing device consisting of a CMOS sensor, and thelike, will be described. In FIG. 25, an optical system of a holographicmemory system (optical information recording and reproducing apparatus)of a coaxial type, referred to as a collinear system, will be described.

This optical information recording and reproducing apparatus performs,for example, the recording and reproducing of information in adisk-shaped hologram recording medium 216. Specifically, a signal beammodulated by information and a reference beam not modulated by theinformation are simultaneously irradiated on the recording medium 216,and are allowed to interfere with each other, so that a volume hologramis formed inside the recording medium 216, and information is recorded.Further, a weak reference beam is irradiated on the recording medium216, so that a reproduced image of the volume hologram is obtained, andthe information is reproduced. Incidentally, the volume hologram of therecording medium is a system, in which an interference fringe is writtenthree-dimensionally by positively using a thickness direction of therecording medium. Also, diffraction efficiency is increased byincreasing the thickness, and a recording capacity is increased by usinga multiplex recording. The digital volume hologram is a hologramrecording system, in which, while using the same recording system as thevolume hologram, image information to be recorded is limited to abinarized digital pattern.

The illustrated optical system comprises a first light source 201generating a laser beam used for recording and reproducing theinformation, a spatial light modulator (hereinafter abbreviated as SLM)204 for modulating the signal beam, and a two-dimensional light sensingdevice 219 for detecting the reproduced beam.

[Recording]

First, a description will be made of a case in which the recording isperformed on a disk-shaped recording medium 216 by using theabove-described optical system.

The light beam emitted from the first light source 201, consisting of agreen laser, and the like, is turned into a parallel light beam by acollimator 202, and passes through a mirror 203, and radiates on thespatial light modulator (SLM) 204. Shown in FIG. 25 is a DMD (DeformableMirror Device), which is used as the SLM 204. Such an SLM 204 has alarge number of light modulators (pixels) two-dimensionally arranged,and represents [0] and [1] per each pixel. In the SLM 204, the lightreflected by the pixel representing the information on [1] is reflectedin the direction of the recording medium 216, and the light reflected bythe pixel representing the information on [0] is not reflected in thedirection of the recording medium 216. In the SLM 204 used by theholographic memory system of a collinear system, its center portion ismade into a portion to modulate an information beam 206, and a portioncircularly surrounding that portion is made into a portion to modulate areference beam 205.

Both of the information beam 206 and the reference beam 205 reflected bythe pixel representing the information on [1] in the SLM 204 transmit apolarizing beam splitter (hereinafter abbreviated as PBS) 207 by Ppolarization. Then, passing through a first relay lens 208, a mirror209, a second relay lens 210, and a dichroic beam splitter (hereinafterabbreviated as DBS) 211, both of the beams are oriented to the recordingmedium 216. The reference beam 205 and the information beam 206, both ofwhich are converted into circularly polarized beams (for example,clockwise circularly polarized beams) by transmitting a quarterwavelength plate (hereinafter abbreviated as QWP) 212, after havingpassed through the DBS 211, are reflected by a mirror 213, and enter anobject lens 214 having a focal length F. The pattern displayed on theSLM 204 forms an intermediate image short of the object lens 214 just byF, by the first and second relay lenses 208 and 210. As a result, a 4Foptical system is configured, in which each of the pattern images (notshown) on the SLM 204, the object lens 214, and the recording medium 216is arranged apart by a distance of F.

The disk-shaped recording medium 216 is rotatably held on a spindlemotor 215. By the object lens 214, the reference beam 205 and theinformation beam 206 are converged on the recording medium 216, and forminterference fringes by mutual interference. A high polymer materialinside the recording medium 216 is recorded with interference fringepatterns at this recording time as a refractive index distribution, and,as a result, a digital volume hologram is formed. By the SLM 204, if theinformation beam 206 is modulated according to the information to berecorded, the recording medium 216 is formed with a digital volumehologram according to that information. Particularly, in the informationbeam area of the SLM 204, if the modulation is performed for each pixelaccording to the information to be recorded, the recording medium 216 isformed with the digital volume hologram having an information amountaccording to the number of such pixels. Incidentally, a reflection filmis provided inside the recording medium 216.

The optical information recording and reproducing apparatus is providedwith a second light source 220, consisting of a red laser, and the like,having no sensitivity for the recording medium 216, other than the firstlight source 201 that performs the recording and reproducing ofhologrammed optical information. By using this second light source 220with the reflection film of the recording medium 216 taken as areference surface, it is possible to detect displacement of therecording medium 216 with a high degree of accuracy. Therefore, even ifside-runout or decentering occurs in the recording medium 216, arecording spot can be allowed to dynamically follow the recording mediumsurface by using optical servo technology, and the interference fringepatterns can be recorded with a high degree of accuracy. Such trackingwill be briefly described below.

A linear polarized light beam emitted from the second light source 220,consisting of the red laser, and the like, transmits a beam splitter(hereinafter abbreviated as BS) 211, and is made into a parallel lightbeam by a lens 222, and is reflected by a mirror 223 and the DBS 211,and is oriented to the recording medium 216. The light beam transmittingthe QWP 212 and converted into a circularly polarized beam (for example,clockwise circularly polarized beam) is reflected by the mirror 213, andenters the object lens 214, and is converged on the reflection film ofthe recording medium 216 as a fine optical spot. The reflected lightbeam becomes a circularly polarized beam (for example, an anticlockwisecircularly polarized beam) rotating in the opposite direction, andenters the object lens 214, again to be made into a parallel light beam,and is reflected by the mirror 213, and transmits the QWP 212, and isconverted into a linear polarized light beam vertical to the polarizedbeam on the outward route. The light beam reflected by the DBS 211,similarly to the outward route, passes through the mirror 223 and thelens 222, and is reflected by the BS 221, and is guided to an opticaldetector 224. The optical detector 224 has a plurality of lightreceiving surfaces, and detects positional information on the reflectedsurface. Based on this detected result, the optical detector can performthe focusing and tracking of the object lens 214. Such focusing andtracking are the same as those performed in the conventionallywell-known optical information recording and reproducing apparatus usingCDs, DVDs, and the like.

[Reproducing]

Next, a description will be made of a case in which reproducing of theinformation recorded in the recording medium 216 is performed by usingthe above-described optical system. The light beam emitted from thefirst light source 201 irradiates the SLM 204 similar to the recordingtime. At the reproducing time, a portion that only modulates thereference beam 205 of the SLM 204 displays the information on [1], andall the portions that modulate the information beam 206 display theinformation on [0]. Consequently, the light only reflected by the pixelof the portion of the reference beam 205 is reflected in the directionof the recording medium 216, and the information beam 206 is notreflected in the direction of the recording medium 216.

The reference beam 205, similar to the recording time, becomes acircularly polarized beam (for example, a clockwise circularly polarizedbeam,) and is converged on the recording medium 216, and reproduces theinformation beam from the recorded interference fringes (digital volumehologram). The information beam reflected by the reflection film insidethe recording medium 216 becomes a circularly polarized beam (forexample, an anticlockwise circularly polarized beam) rotating in theopposite direction, and enters the object lens 214 again to be made intoa parallel light beam, and is reflected by the mirror 213, and transmitsthe QWP 212, and is converted into a linear polarized light beam (Spolarized beam) vertical to the outward polarized beam. At this time, anintermediate image of the display pattern of the SLM 204, reproducedfrom the object lens 214 at a distance of F, is formed.

The light beam transmitting the DBS 211 passes through the second relaylens 210, the mirror 209, and the first relay lens 208, and is orientedto the PBS 207. The light beam reflected by the PBS 207 is re-imaged asthe intermediate image of the display pattern of the SLM 204 at aposition conjugated with the SLM 204. At this position, there is anopening 17 placed in advance, which shades an unnecessary reference beamexisting in the periphery area of the information beam. By the lens 218,the re-imaged intermediate image forms the display pattern of the SLM204 of the information beam portion only on the light sensing device 219of the CMOS sensor, and the like. As a result, the unnecessary referencebeam 205 does not enter the light sensing device 219, and, therefore,the reproduced signal of a good S/N (signal to noise ratio) can beobtained.

First Embodiment

First, a concept of the correction of a positional shift in the presentinvention will be described. In a holographic memory system, due tovarious factors, the positional shift may be generated in the positionalrelationship between the light beam incident on a two-dimensionalspatial light modulator (SLM) and a spatial light modulator. The presentinvention corrects this shift or attempts compensation for this shift.The correction of the positional shift will be described below by usingFIGS. 1 to 3.

FIGS. 1A to 1C show a case wherein the positional relationship betweenan incident beam on the SLM and the SLM is according to a design. Asshown in FIG. 1A, a two-dimensional SLM comprises a square effectivepixel area, and inside this effective pixel area, is arranged a largenumber of pixels in a matrix pattern. The incident beam is circular, andits diameter is smaller than the effective pixel area of the SLM. If thepositional relationship is according to the design, the incident beamhits against the center of the pixel area. As described in the paragraphof the Related Art discussed above, though the SLM is set with aninformation beam area and a reference beam area surrounding the former,an example of the arrangement of the information beam area and thereference beam area is shown as an area of the pixel for an informationbeam and an area of the pixel for a reference beam in FIG. 1B. Here, acoordinate is set as shown in a horizontal direction and a verticaldirection. FIG. 1C shows the incident beam and the relationship betweenthe information beam area and the reference beam area in the casewherein the positional relationship is correct. The outer periphery ofthe reference beam is along the circle, and the diameter of this circleis slightly smaller than the diameter of the outer periphery circle ofthe incident beam. If the positional relationship is correct, the outerperiphery circle of the incident beam and the outer periphery circle ofthe reference beam are concentric, and the circle of the reference beamarea are concentric, and the circle of the reference beam is completelyincluded in the circle of the incident beam.

In contrast to this, FIGS. 2A to 2C show a case in which the positionalshift occurs between the incident beam and the SLM. FIG. 2A shows a casein which the incident beam hits, but is out of touch with, a center ofthe effective pixel area of the SLM. Even in this case, as shown in FIG.2B, the information beam area and the reference beam area are, similarto the case of FIG. 1B, arranged with the center point of the effectivepixel area of the SLM as a center. As a result, as shown in FIG. 2C, theincident beam hits by displacing from the information beam area and thereference beam area, and particularly, the incident beam does not hit apart of the reference beam area. If, in this state, a part of thereference beam to be incident on the recording medium is missing, and,therefore, the original hologram information cannot be recorded if atthe recording time, and, if at the reproducing time, a recorded normalhologram cannot be reproduced.

Hence, in the present embodiment, the positional shift in the incidentbeam is detected, and the positional shift amount is fed-back so as toperform the correction based on that positional shift amount, therebypreventing the positional shift between the incident beam and theinformation beam area, and the reference beam area from occurring. FIGS.3A to 3C are views explaining this correction. FIG. 3A, similar to FIG.2A, shows that the incident beam hits by displacing from the effectivepixel area of the spatial light modulator. Hence, in the presentembodiment, upon detecting the direction and magnitude of the positionalshift of the incident beam, the positions of the information beam areaand the reference beam area in the spatial light modulator are alsoshifted by that detected direction and magnitude, as shown in FIG. 3B.As a result, as shown in FIG. 3C, the information beam area and thereference beam area are put into a normal relationship for the incidentbeam. As a result, at the recording time, normal recording can beperformed, and at the reproducing time, also, normal reproducing can beperformed.

In the present embodiment, as the spatial light modulator, for example,the DMD described above in the paragraph of the Related Art, areflection type light interference modulator, to be described later, ora reflection type liquid crystal on silicon (LCOS) can be used.Whichever spatial light modulator is used, modulation information on theinformation beam and the reference beam is given to each pixel. In thespatial light modulator, shift registers for the horizontal directionand the vertical direction are arranged on the periphery of theeffective pixel area, and information as to whether each pixel is putinto a state of [1] or [0] is written in these shift registers, forexample, as the information on voltage. Then, based on the data storedin these shift registers, each pixel is driven, so that each pixel isput into whichever states of [1] or [0]. Hence, by changing each pixelaccording to the shift amount detecting a read start position from theshift register, it is possible to effectively shift the positions of theinformation beam area and the reference beam area in the spatial lightmodulator, and to perform the correction according to the shift of theincident beam.

When the DMD is used as the spatial light modulator, in the case of thepixel put into [1], the mirror is oriented toward the normal reflectiondirection, and in the case of the pixel put into [0], the mirror isoriented toward the direction other than the reflection direction, andonly the light from the pixel oriented towards the normal reflectiondirection is oriented to the recording medium. In the case of thereflection type light interference modulator, in the case of the pixelput into [1], the reflectance by the interference becomes high, and inthe case of the pixel put into [0], the reflectance becomes low, and thereflection beam from such a reflection type light interference modulatoris oriented to the recording medium. In the case of the reflection typeliquid crystal on silicon, in the case of the pixel put into [1], thepixel is displayed white, due to the relationship between a polarizedfilter and a test plate by the control of retardation of the liquidcrystal, and in the case of the pixel put into [0], the pixel isdisplayed black, contrariwise, and the light from the pixel displayedwhite is oriented to the recording medium.

Next, the optical system of the optical information recording andreproducing apparatus of the first embodiment will be described. In theoptical information recording and reproducing apparatus of the presentembodiment, the spatial light modulator and the light sensing device maybe separately provided or the spatial light modulator and the lightsensing device may be provided as a modulator/light sensing deviceintegrated on the same semiconductor substrate. Further, though thisoptical information recording and reproducing apparatus has a shiftamount detector that detects a shift of the positional relationshipbetween the incident beam and the spatial light modulator, in the caseof using the modulator/light sensing device, the apparatus may beseparately provided from the modulator/light sensing device, or themodulator/light sensing device may be allowed to function as a shiftamount detector, when the spatial light modulator and the light sensingdevice are separately provided from the spatial light modulator and thelight sensing device.

FIGS. 4 to 9 explain the optical system of the optical informationrecording and reproducing apparatus of the first embodiment. The opticalinformation recording and reproducing apparatus of the presentembodiment performs the recording of the information, for example, bywriting a volume hologram in a disk-shaped hologram recording medium186, and by obtaining the reproduced image of the volume hologram,reproducing of the information is performed. The illustrated opticalsystem comprises a first light source that generates a laser beam usedfor the recording and reproducing of the information, a modulator/lightsensing device (SLM/CMOS) integrally provided with a spatial lightmodulator (SLM) for modulating a signal beam, a two-dimensional lightsensing device for detecting a reproduced beam, and a shift amountdetector that detects a shift amount for the modulator/light sensingdevice of the light beam incident on the modulator/light sensing device.FIGS. 4 and 5 show the optical system from the light source at therecording time to the spatial light modulator (modulator/light sensingdevice). FIG. 4 shows a case wherein the shift amount detector isprovided separately from the modulator/light sensing device, and FIG. 5shows a case wherein the modulator/light sensing device also comprisesthe functions of the shift amount detector. FIG. 6 shows the opticalsystem from the spatial light modulator (modulator/light sensing device)at the recording time to the recording medium (hologram disk). FIGS. 7and 8 show the optical system from the light source at the reproducingtime to the spatial light modulator (modulator/light sensing device).FIG. 7 shows a case wherein the shift amount detector is providedseparately from the modulator/light sensing device, and FIG. 8 shows acase wherein the modulator/light sensing device also has the functionsof the shift amount detector. FIG. 9 shows an entirety of the opticalsystem subsequent to the shift correction at the reproducing time.

First, by using FIGS. 4 to 6, a description will be made of a case inwhich the recording is made on a recording medium 118, which is thehologram disk. In FIG. 4, the light beam emitted from a first lightsource 101, consisting of a green laser, and the like, is made into aparallel light beam by a collimator 102, and enters a mask element 103.The mask element 103 has the functions of masking a portion equivalentto the information beam of the center portion of the light beam. As themask element 103, for example, the liquid crystal on silicon type can beused. The mask that shields the center portion of the light beam may beinserted into the optical path. At the time of recording theinformation, this mask element 103 does not function, but allows all thelight beams to transmit. The light that transmits the mask element 103enters a polarized beam splitter (hereinafter abbreviated as PBS) 104.

From among the light beams having entered the PBS 104, a P polarizedcomponent passes through there as it is, but an S polarized component isreflected, and the component shown in FIG. 4 enters a shift amountdetector 124. The shift amount detector 124 is composed of atwo-dimensional CMOS-sensor, and the like, and detects the shift amountin the incident beam by measuring a position of the incident beam on theshift amount detector 124.

The light beam having transmitted the PBS 104 by the P polarizationtransmits a quarter wave plate (hereinafter abbreviated as QWP) 105, andpasses through a first relay lens 106 and a second relay lens 107, andis irradiated on a modulator/light sensing device 108 (FIG. 4) mountedwith a spatial light modulator (SLM) and a CMOS sensor by one chip or amodulator/light sensing device 108 (FIG. 4) mounted with a spatial lightmodulator (SLM) and a CMOS sensor by one chip or a modulator/lightsensing device 108′ (FIG. 5). When a light interference modulator (iMOD)configured not to allow a polarized state to be changed as the SLM isused, the QWP 105 may be provided in advance at an in-plane settingangle, in which the linear polarized light changes 90° forward andbackward. Further, in the case of a reflection type liquid crystal onsilicon (LCOS) configured to allow the polarized state to change 90° asthe SLM, the QWP 105 is not required. However, in reality, due to thedesign of the SLM, refraction with the actual thing, and differences inthe thickness of the liquid crystal, and the like, and moreover, in thecase of the liquid crystal, due to the necessity of slightly (severaldegrees) inclining the orientation of the liquid crystal in an initialstate, referred to as a pre-tilt, some reflections from the PBS 104 areobserved at the time of the black [0], and a contrast of the white/blackbecomes smaller. When this contrast is not permitted in terms of thesystem, the QWP 105 is installed in order to make some reflections fromthe PBS 104 at the time of the black [0] into the minimum value, therebyadjusting the in-plane setting angle. Here, the light interferencemodulator (iMOD) is an element having a reflection electrode and asemi-transparent film arranged in front of the reflection electrode. Thesemi-transparent film has the functions of allowing the incident beam totransmit at some ratios and reflecting the remaining beam. This lightinterference modulator performs a light modulation by using theinterference between the reflection beam from the semi-transparent filmsurface when the light enters from the semi-transparent film side, andthe reflection beam having transmitted the semi-transparent film andreflected by the reflection electrode. The reflection electrode has alsoa property of reflecting the light. Here, by changing a distance of thespace (air gap) between the semi-transparent film and the reflectionelectrode, the reflectance as an entirety of the incident beam can becontrolled, and intensity of the reflection beam can be modulated. Thedistance of the air gap can be controlled in such a manner that a signalvoltage is applied between the semi-transparent film and the reflectionelectrode, and the semi-transparent film is displaced by Coulomb forceby an electrical field generated by the signal voltage. As thesemi-transparent film, a thin film of Ti (titanium) can be preferablyused.

In the optical system shown in FIG. 5, the incident beam having enteredthe modulator/light sensing device 108′ is detected, so that the shiftamount for the modulator/light sensing device 108′ is detected. When theSLM and the light sensing device, which are superposed in a longitudinaldirection for each pixel so that the SLM comes to the incident beamside, are used, similar to the reproducing time of the reproduced lightfrom the recording medium, all the pixels are uniformly put into atransmission mode.

In the cases shown in FIGS. 4 and 5, according to the detected shiftamount (shift direction and magnitude), a correction of the shift of thepositional relationship between the information beam area and thereference beam area of the modulator/light sensing device 108 (108′) andthe incident beam is performed. As a method of the shift correction, inaddition to shifting a start position in the above-described shiftregister, there is also a method of holding the modulator/light sensingdevice 108 (108′), for example, on an XY stage, and changing thephysical position of the modulator/light sensing device 108 (108′) byoperating the XY stage.

Hereafter, a description will be made separately of a case (iMOD/CMOS),in which the element consisting of the combination of the iMOD and theCMOS is used as the modulator/light sensing device 108, and the case(LCOS/CMOS), in which the element consisting of the combination of theLCOS and the CMOS is used.

The case of iMOD/CMOS:

The light beam having transmitted the QWP 105 is converted into acircularly polarized beam (for example, a clockwise circularly polarizedbeam), and passes through the first relay lens 106, and the second relaylens 107, and is irradiated on the modulator/light sensing device 108.The light reflected by the pixel representing the information on [1(white)] by the SLM of the modulator/light sensing device 108 isreflected in the direction of the recording medium 118 with a highreflectance, and the light reflected by the pixel representing theinformation on [0 (black)] of the SLM is only slightly reflected in thedirection of the recording medium 118 by the interference. Similar tothe conventional example, the SLM of the collinear system is providedwith a portion to modulate the information beam 110 and a portion tomodulate the reference beam 109 circularly surrounding the informationbeam.

Described below, by referring to FIG. 6, the light beam reflected by theSLM of the modulator/light sensing device 108 becomes a circularlypolarized beam rotated in an opposite direction (for example, ananticlockwise circularly polarized beam). The light beam having passedthrough the second relay lens 107 and the first relay lens 106 transmitsthe QWP 105, and is converted into an S polarized beam, and is reflectedby the PBS 104, and is oriented in the direction of the recording medium118.

The case of LCOS/CMOS:

On the other hand, when the LCOS/CMOS is used as the modulator/lightsensing device 108, the light beam having passed through the PBS 104passes through the first relay lens 106 and the second relay lens 107,and irradiates the modulator/light sensing device 108. The lightreflected by the pixel representing the information on [1 (white)] onthe SLM is converted into an S polarized beam, and the light reflectedby the pixel representing the information on [0 (black)] holds a stateof the P polarized beam. Similar to the conventional example, a portionto modulate the information beam 110 and a portion to modulate thereference beam 109 circularly surrounding the information beam areprovided on the SLM of the collinear system.

Described below, by referring to FIG. 6, from among the light beams, theS polarized beam is reflected by the PBS 104, and is oriented toward therecording medium 118, and the P polarized beam transmits the PBS 104,and is not oriented toward the recording medium 118.

Even when the iMOD/CMOS is used or the LCOS/CMOS is used, the referencebeam 109 and the information beam 110 reflected by the pixelrepresenting the information on [1 (white)] in the SLM of themodulator/light sensing device 108 are reflected by the PBS 104, and areoriented toward the recording medium 118 by passing through a thirdrelay lens 111, a mirror 112, a fourth relay lens 113, and a dichrolicbeam splitter (hereafter abbreviated DBS) 114, and are reflected by amirror 115, and enter an object lens 116 of the focal length F. Thepatterns displayed in the SLM of the modulator/light sensing device 108form an intermediate image in front of the object lens 116 just by F bythird and fourth relay lenses 111 and 112. As a result, a 4F opticalsystem is configured in which each of the pattern images (not shown) onthe SLM of the modulator/light sensing device 108, the object lens 116,and the recording medium 118 is arranged apart just by a distance of F.

The disk-shaped recording medium 118 is rotatably held on a spindlemotor 117. By the object lens 116, the reference beam 109 and theinformation beam 110 are converged on the recording medium 118, and forman interference fringe by mutual interference. A high polymer materialinside the recording medium 118 is recorded with interference fringepatterns at this recording time as a refractive index distribution, anda digital volume hologram is formed. If the information beam 110 ismodulated according to the information to be recorded, the recordingmedium 118 is formed with the digital volume hologram according to thatinformation. Incidentally, a reflection film is provided inside therecording medium 118.

This optical information recording and reproducing apparatus is providedwith a second light source 119 consisting of a red laser, and the like,having no sensitivity for the recording medium 118, other than the firstlight source 101 that performs the recording and reproducing of thehologrammed optical information. By using this second light source 119with the reflection film of the recording medium 118 taken as areference surface, it is possible to detect displacement of therecording medium 118 with a high degree of accuracy. Therefore, even ifside-runout or decentering occurs in the recording medium 118, arecording spot can be allowed to dynamically follow the recording mediumsurface by using optical servo technology and the interference fringepatterns (digital volume hologram) can be recorded with a high degree ofaccuracy. Such tracking will be briefly described below.

The light beam emitted from the second light source 119 transmitsthrough a beam splitter (hereinafter abbreviated as BS) 120, and is madeinto a parallel light beam by a lens 121, and is reflected by a mirror122 and the DBS 114, and is oriented to the recording medium 118. Afterthat, the light beam is reflected by the mirror 115, and enters theobject lens 116, and is converged on a reflection film of the recordingmedium 118 as a fine optical spot. The reflected light beam enters theobject lens 116 again to be made into the parallel light beam, and isreflected in order by the mirror 115 and the DBS 114, and, similar tothe outward route, passes through the mirror 122 and the lens 121, and apart of the light beam is reflected by the beam splitter BS 120, and isguided to a light detector 123. The light detector 123 has a pluralityof light receiving surfaces, and detects the positional information onthe reflection surface by the known method, and based on this detection,performs focusing and tracking of the object lens 116.

Next, by using FIGS. 7 to 9, a description will be made of a case inwhich the reproducing of the recording information is performed from therecording medium (hologram disk) 118.

The light beam emitted from the first light source 101 is irradiated onthe modulator/light sensing device 108, similar to the recording time.At this time, the intensity of the light from the first light source 101is less than the intensity used at the recording time, so that theinformation is recorded in the recording medium 118 is not destroyed. Inthe present embodiment, even when performing the reproduction, thedetection of the shift in the incident beam is performed. As shown inFIG. 7, the light beam emitted from the first light source (green laser)101 enters the PBS 104, and similar to the recording time, the lightbeam having transmitted the PBS 104 by P polarization enters themodulator/light sensing device 108. In contrast to this, the polarizedbeam of the S polarization is reflected by the PBS 104, and enters theshift amount detector 124, thereby detecting the shift amount.Alternatively, as shown in FIG. 8, the shift amount is detected by theincident beam having transmitted the PBS 104 and enters themodulator/light sensing device 108′. When the element is used, in whichthe SLM and the light sensing device are superposed in a longitudinaldirection for each pixel, so that the SLM comes to the incident beamside as the modulator/light sensing device 108′, similar to thereproducing time of the reproduced beam from the recording medium, allthe pixels are uniformly put into a transmission mode. In the casesshown by FIGS. 7 and 8, a correction of the shift of the positionalrelationship between the modulator/light sensing device 108 (108′) andthe incident beam is performed according to the detected shift amount(shift direction and magnitude) similar to the case of recording.

At the reproducing time, the mask element 103 masks a portion equivalentto the information beam of the center portion of the light beam. In thepresent embodiment, the liquid crystal on silicon configuring the maskelement 103 allows the center portion only of the light beam to rotate90° in a polarized direction, so as to be made into the S polarizedbeam, and this beam is reflected by the subsequent PBS 104, such that itdoes not reach the modulator/light sensing device 108. In the maskelement 103, the position in which the light beam is masked changesaccording to the detected shift amount, and, even when the light beam isshifted, the portion equivalent to the information beam is certainlymasked. Further, the mask shielding the center position may be insertedinto the optical path. When the mask is inserted, a mask position alsocan be moved to the measured quantity of the shift amount.

Assuming that the shift correction is performed as described above, thefirst relay lens 106 and the second relay lens 107 have the task offorming the image of the mask element 103 on the SLM of themodulator/light sensing device 108 (108′). As a result, the element onlyin the portion of the reference beam is irradiated, and the portion ofthe information beam is accurately shielded by the image of the maskelement 103. In the SLM of the modulator/light sensing device 108, onlythe portion that modulates reference beam 109 displays the informationon [1 (white)], and the portion that modulates the information beam 110all display the information on [0 (black)]. Consequently, only the lightreflected by the pixel in the portion that modulates the reference beam109 is reflected in the direction of the recording medium 118. The lightbeam of the pixel in the portion that reflects the information beam 110is neither reflected in the direction of the recording medium 118, noris it even radiated by nature, and therefore, the information beamhaving a much better S/N ratio can be produced as compared to theconventional example.

The reference beam 109 similar to the recording time is reflected by thePBS 104, and is converged on the recording medium 118, and theinformation beam is reproduced from the recorded interference fringes.The information beam (that is, the reproduced beam) reflected by thereflection film inside the recording medium 118 re-enters the objectlens 116 so as to be made into the parallel light beam, and is reflectedby the mirror 115. At this time, an intermediate image of the displaypattern of the SLM reproduced at a distance of F from the object lens116 is formed.

The light beam having transmitted the DBS 114 is oriented to the PBS 104by passing through the fourth relay lens 113, the mirror 112, and thethird relay lens 111, and is re-imaged (not shown) as an intermediateimage of the display pattern of the SLM at the position conjugated withthe mask element 103 by the fourth relay lens 113 and the third relaylens 111. This re-imaged intermediate image is reflected by the PBS 104,and is imaged on the modulator/light sensing device 108 (108′) by thefirst relay lens 106 and the second relay lens 107. Incidentally, in thepresent embodiment, a CMOS sensor comprising a photo diode and a MOStransistor that amplifies the light receiving signal detected by thephoto diode for each pixel as the light sensing device, is used.Moreover, in the present embodiment, since an element that provides thespatial light modulator (SLM) and the light sensing device, such as theCMOS sensor, or the like, on the same chip is used as themodulator/light sensing device 108, there is no need for a complicatedmechanism to position both of them. Further, this can lead to thecost-cutting and miniaturization of the optical system.

In the optical information recording and reproducing apparatus of thepresent embodiment, since the shift of the positional relationshipbetween the light beam before receiving the modulation by the SLM andthe SLM can be corrected both at the recording time and reproducingtime, a recording error and a reproducing error can be decreased to alarge extent.

Such a mechanism that corrects the shift of the positional relationshipbetween the incident beam and the spatial light modulator also can beadapted to the optical system in which the spatial light modulator andthe light sensing device are provided separately. FIG. 10 shows anoptical system from the light source at the recording time until thespatial light modulator in the case when the shift amount detector isadded to the conventional optical system using the DMD as the spatiallight modulator. This optical system inserts the PBS 225 in the midst ofthe optical path between the collimator 202 and the mirror 203 in theoptical system shown in FIG. 25, and the S polarized component reflectedby the PBS 225 is allowed to enter the shift amount detector 124,thereby detecting the shift amount. Even in this optical system, basedon the detected shift amount, the correction of the shift is performedat the recording time and the reproducing time. In this optical system,as the spatial light modulator (not integrated with the light sensingdevice), the reflection type light interference modulator and thereflection type liquid crystal on silicon also can be used.

Next, a detection method of the shift amount will be described. As thedetection method of the shift amount, though a variety of methods areconceivable, for example, there is such a method as described below.

The shift amount detector 124 comprises the light sensing device, suchas photo diodes arranged in a matrix pattern, and the like. FIG. 11shows an arrangement of pixels in the shift amount detector 124, and inthe Figure, a small quadrangle 302 shows an area for one pixel portion.When the modulator/light sensing device 108′ is used as the shift amountdetector, the same is true in this case. An area 305 dividing theeffective pixel area of the shift amount detector 124 into four equalportions up and down and left and right is considered. This area isshown by a thick line in FIG. 11. Further, a circle 301 in FIG. 11 showsan incident beam 301, which ideally hits the center of the spatial lightmodulator (modulator/light sensing device 108 and 108′), and a circle303 arranged by displacing from the circle 301 shows an incident beam,of which a positional relationship is shifted from the spatial lightmodulator, while an area 304 shows the pixels which the shift light beam301 has hit.

In each of the four areas 305, the number of pixels (the pixel 304 inthe Figure) which have received the light at equal to or more than acertain threshold value is determined, and from the difference in thenumber of pixels, the shift amount can be determined. The calibrationrelationship between the difference in the number of pixels and theshift amount is determined in advance, and its calibration relationshipmay be stored in a feedback mechanism for the shift amount correction.

FIGS. 12A and 12B show one example to determine the shift amount in thecase in which the incident beam is shifted from the center of thespatial light modulator just only to the left and below (a and b). FIG.12A shows a case in which the shift in the X axis (horizontal) directionis determined, and FIG. 12B shows a case in which the shift in the Yaxis (vertical) direction is determined. Describing the case of the Xaxis, when the four areas 305 are divided into the right and the left,the area of the incident beam irradiated on each area is determined,which is substantially represented by the number of pixels havingreceived the light (the number of the pixel 304). Here, when theincident beam is taken as a circle of a radius r, an area superposed onthe right or left area (the number of pixels) is determined. As shown inTable 1, a ratio of the left and right areas is similarly decided bya/r. Since the radius r is decided by the sum of the left and rightareas, if the left and right areas are known, the shift amount a isuniquely decided. Also with respect to the Y axis direction, the shiftamount can be determined by the same procedure.

TABLE 1 a/r Ratio(right/left) 1 0.9 1.90E−02 0.8 5.49E−02 0.7 1.04E−010.6 1.66E−01 0.5 2.43E−01 0.4 3.37E−01 0.3 4.53E−01 0.2 5.96E−01 0.17.74E−01 0 1.00E+00 −0.1 1.29E+00 −0.2 1.68E+00 −0.3 2.21E+00 −0.42.96E+00 −0.5 4.12E+00 −0.6 6.02E+00 −0.7 9.63E+00 −0.8 1.82E+01 −0.95.25E+01 −1

Further, in the example shown in FIG. 13, X-Y axes 306, with the centerof the spatial light modulator as an origin is considered, and anisointensity line 307, and the like, of the received light beam (shiftedlight beam) is considered. The distribution of the pixels in which anincident beam intensity is equal is supposed to draw a circle if theincident beam is circular. From the minimum value min(x) and the minimumvalue max(y) of the coordinate of such a pixel in the axis X directionand the minimum value min(y) and the maximum value max(y) in the axis Ydirection, the shift amount can be determined as follows:

The shift in the axis X direction=(max(X)+min(X))/2.

The shift in the axis Y direction=(max(y)+min(y))/2.

Assuming that the shift of the incident beam is measured by using such atechnique or another technique, the shift correction is performed. Inthe shift correction, when the modulation information for an informationbeam and a reference beam is displayed in the spatial light modulator,the start positions of the shift registers arranged in every directionof the periphery of the effective pixels of the spatial light modulatorare shifted. As shown in FIG. 14, after measuring the shift amount withwhich the incident beam has shifted, the start position of the shiftregister was shifted from an initial position 310 of the initial settingto a position 311 after the correction according to the shift amount. Asa result, the positions of the pixel 308 for the information beam andthe pixel 309 for the reference beam are also shifted, and are adaptedto the shifted light beam 303. As a result, both the information beamand the reference beam are normally modulated, and the recording andreproducing are normally performed.

FIG. 15 shows an equivalent circuit of the spatial light modulator inthe present embodiment. Though, in reality, the modulator/light sensingdevice in which the spatial light modulator and the light sensing deviceare integrated is used, here, a portion regarding the spatial lightmodulator only is shown in order to describe only the change of thestart position of the shift register. Each of the pixels is configuredby a switching transistor 3, an interference structure portion 4, aretention capacity 5, and a common counter electrode 6 of theinterference structure portion, and such pixels are arranged in a matrixpattern. For the selection of the pixels, a plurality of vertical signallines 1 extending in the illustrated vertical direction (columndirection) and a plurality of drive lines 2 extending in the horizontaldirection (row direction) are provided. One end of the drive line 2 isconnected to a vertical shift register 7, and one end of the verticalsignal line 1 is connected to a horizontal shift register 8 through asampling switch 9. A shift register 8 is provided in order to drive thesampling switch 9. Although the detail of the configuration andoperation of such a spatial light modulator will be described later,when the start position of the vertical shift register of the initialsetting is taken as 7 a and the start position of the horizontalregister as 8 a, the pixel surrounded by a solid line is the start pixelof the spatial light modulator in the initial state. When the shift ofthe incident beam is measured as -two pixels in the vertical directionand -three pixels in the vertical direction, that positional shiftamount (-two pixels and -three pixels) is fed back to the shiftregister, and the start position of each shift register is taken as 7 band 8 b, so that the pixel surrounded by a broken line becomes the startpixel. In this manner, the display positions of the modulationinformation on the information beam and the reference beam can bechanged.

Next, the circuit operations of the recording and reproducing in theoptical information recording and reproducing apparatus of the presentembodiment will be described. FIG. 16 is an equivalent circuit diagramfor explaining the modulator/light sensing device integrating the SLMusing a reflection type light interference modulator or a reflectiontype liquid crystal on silicon and the light sensing device consistingof the CMOS sensor used in the present embodiment. In FIG. 16, referencenumerals 1 to 10 are given to the component parts relating to thespatial light modulator, and reference numerals 21 to 33 are given tothe component parts relating to the light sensing device configured asthe CMOS sensor.

A plurality of vertical signal lines, 1, 1 a, . . . extending in thecolumn direction (illustrated vertical direction) and a plurality ofhorizontal drive lines 2, 2 a, . . . extending in the row direction(illustrated horizontal direction) are provided, and these linesconfigure matrix wirings, and the intersecting point with the verticalsignal line and the drive line corresponds to each pixel. Consequently,the pixels are arranged in a matrix pattern, the vertical signal line isprovided for each column of the pixel arrangement, and the drive line isprovided for each row. The vertical signal lines 1, 1 a, . . . are forthe spatial light modulator, and similarly to this, the vertical signallines 26, 26 a, . . . for the light sensing device are provided for eachrow. Further, the horizontal read lines 27, 27 a, . . . horizontal resetlines 28, 28 a, . . . , and horizontal selection lines 29, 29 a, . . .are provided for the light sensing device for each column.

For the spatial light modulator, each pixel is provided with pixelswitches 3, 3 a, . . . comprising switching transistors, interferencestructure portions (or liquid crystal portions) 4, 4 a, . . . , andretention capacities 5, 5 a, . . . . Further, for the spatial lightmodulator, each pixel is provided with photodiodes 21, 21 a, . . . ,transfer switches 22, 22 a, . . . comprising transistors, reset switches23, 23 a, . . . comprising transistors, amplifier transistors 24, 24 a,. . . , and selection switches 25, 25 a, . . . comprising transistors.When the spatial light modulator comprises the reflection type lightinterference modulator, the interference structure portion is used, andwhen it comprises the reflection type liquid crystal on silicon, theliquid crystal portion is used.

In the spatial light modulator portion of each pixel, gates of the pixelswitches 3, 3 a, . . . are connected to the corresponding drive lines 2,2 a, . . . , and drains are connected to the corresponding verticalsignal lines 1, 1 a, . . . . The retention capacities 5, 5 a, . . . areprovided between the source of the pixel switch and the constantpotential point (for example, an earth potential point). Further, theinterference structure portions (or liquid crystal portions) 4, 4 a, . .. are also connected to the source of the pixel switch. Eachinterference structure portion (or the liquid crystal portion) alsocomprises a common counter electrode 6 common for each pixel. One end ofeach of the vertical signal lines 1, 1 a, . . . is connected to thehorizontal signal line 10 for the spatial light modulator through thesampling switches 9, 9 a, . . . , and the gates of the sampling switches9, 9 a, . . . are connected to horizontal shift register 8 of thespatial light modulator. Further, one end of each of the drive lines 2,2 a, . . . is connected to vertical shift register 7.

In the light sensing device portion of each pixel, anodes of thephotodiodes 21, 21 a, . . . are earthed, and each of cathodes areconnected to one end of the transfer switches 22, 22 a, . . . ,respectively. The gates of the transfer switches 22, 22 a, . . . areconnected to the corresponding horizontal read lines, and the other endeach is connected to one end each of the reset switches 23, 23 a, . . .are for resetting the photodiodes and floating diffusion (FD) areaselectrically connected with the photodiodes to a predeterminedpotential, and the other ends are applied with a predetermined potentialand the gates are connected to the horizontal reset lines. Further, theother ends of the transfer switches 22, 22 a, . . . are also connectedto the gates of the amplifier transistors 24, 24 a, . . . for amplifyingthe signal charges by the photodiodes 21, 21 a, . . . . One end each ofthe amplifier transistors 24, 24 a, . . . is applied with thepredetermined potential, and each of the other end is connected to thecorresponding vertical signal line of the light sensing device throughthe selection switches 25, 25 a, . . . . The gate of the selectionswitch is connected to the corresponding horizontal selection line. Oneend each of the vertical signal lines 26, 26 a, . . . of the lightsensing device is connected to the horizontal signal line 33 of thelight sensing device through the sampling switches 32, 32 a, . . . . Thegates of the sampling switches 32, 32 a, . . . are connected to thehorizontal shift registers 31 of the light sensing device. Each one endof the horizontal read lines 27, 27 a, . . . , the horizontal resetlines 28, 28 a, . . . , and the horizontal selection lines 29, 29 a, . .. for the light sensing device is connected to the vertical shiftregister 30 of the light sensing device, respectively.

In FIG. 16, while the pixels are arranged in two rows and two columns,as a matter of course, the circuit of the modulator/light sensing device108 (108′) in the optical information recording and reproducingapparatus of the present embodiment can be, for example, made into amatrix configuration of multi-pixels such as 1,000 rows and 1,000columns.

The circuit operation of the modulator/light sensing device 108 of thepresent embodiment will be described. First, a write mode will bedescribed. The operation of the write time is the same operation as theactive matrix operation in the general display device, and the like.

First, an ON signal is inputted to the drive line 2 from the verticalshift registers 7, and pixel switches 3 and 3 a are put into an ONstate. In this state, the horizontal shift registers 8 are operated inorder and a signal is transmitted to the vertical signal line 1 from thehorizontal signal line 10. That is, first, the sampling switch 9 isturned on, and the signal of the horizontal signal line 10 is written inthe vertical signal line 1, and the retention capacity 5 is accumulatedwith the charge according to the signal through the pixel switch 3. Whenthe reflection type light interference modulator is used as the SLM, thepotential difference between the reflection electrode (not shown) of theinterference structure portion 4 and the common counter electrode 6 isapplied to this modulator, and an electrical field is generatedtherebetween. By this electrical field, the interference structureportion 4 is changed, and specifically, the distance between thereflection electrode and the common counter electrode 6 is changed, andthe reflectance for the incident beam can be changed to a desired value.Here, if the reflection type liquid crystal on silicon is used as theSLM, one electrode of the liquid crystal pixel is connected to the pixelswitch, and the other electrode is made into the common counterelectrode 6, so that the electrical field is generated in the liquidcrystal portion, and by this electrical field, the orientation of theliquid crystal is changed, thereby changing the polarizationcharacteristics of the incident beam. By the combination of thepolarization plate, the wave length plate, and the like, the reflectanceis changed to the desired value. As the SLM in the holographic memorysystem, since two gradations of white and black may be enough, thevoltage in which the maximum reflectance or the minimum reflectance canbe obtained as the reflectance is given to the interference structureportion 4 or the liquid crystal portion.

After having written one line all, the drive line 2 is turned off, andthis time, signals are inputted to the drive line 2 a in order to putpixel switches 3 b and 3 c into an on state. After that, similarly asdescribed above, the signals are written into the pixels in order in thehorizontal direction. After the voltage is written in all the line, thisoperation is repeated from the first line again, and the voltage of eachpixel is re-written. In this manner, the signals are written in all thepixels, and after that, if the light from the first light source 101 isallowed to enter the modulator/light sensing device 108, it is reflectedin each pixel as a modulated light, and this reflected lightinterferences with the reference beam 109, and is recorded in therecording medium 118.

In the modulator/light sensing device 108, the pixel that modulates thereference beam 109, that is, the pixel located in the reference beamarea is set so as to have a constant reflectance. For example, the pixelis made into the same configuration as the pixel hit by the informationbeam and given a voltage such that the maximum reflectance is obtained.Needless to mention, since the shift correction is performed asdescribed above, the pixel modulating the reference beam 9 is not alwaysthe same.

Next, a read mode will be described.

The information recorded on the recording medium 118 is reproduced bythe reference beam 109, and a beam intensity equivalents to [1 (white)]or [0 (black)] enters the light sensing device, and an amount of chargecorresponding to that beam intensity is accumulated in the photodiodes21, 21 a, . . . . An ON signal is outputted to the horizontal read line27 from the vertical shift register 30 and the transfer switch 22 isturned on, so that the charge accumulated in the photodiode changes thepotential of the gate of the amplifier transistor 24. As a result, thevoltage corresponding to the signals accumulated in the photodiode isoutputted to the drain of the amplifier transistor 24. When theselection switch 25 is put into an on state by the horizontal selectionline 29 from the vertical shift register 30, the output of the amplifiertransistor 24 is transmitted to the vertical signal line 26. Thehorizontal shift transistor 31 is operated in order, and the samplingswitch 32 is turned on, so that information is transmitted to ahorizontal signal line 33 from the vertical signal line 26. After thesampling switch 32 is turned off, the sampling switch 32 a of the nextcolumn is turned on, and the signal is transmitted in the same manner.After all the signals of one column are transmitted, the transmissionproceeds to the next column by the vertical shift register 30, and inthe same manner, the signal is read in order. After that, based on theread signal, the signals recorded on the recording medium 118 are onlyto be read.

Incidentally, when the SLM using the reflection type light interferencelight modulator and the CMOS sensor, which is the light sensing device,are laminated and integrated on a silicon substrate, the light sensingdevice is also positioned at the bottom of the above-describedsemi-transparent film of the interference structure portion.Consequently, immediately before the read mode is performed, it isnecessary that the transistors 3, 3 a, 3 b, . . . of the SLM of all thepixels receiving information are turned on once, and the interferencestructure portions 4, 4 a, 4 b, . . . are kept in a state showing thesame level of transmittance.

Incidentally, the circuit diagram shown in FIG. 4 can be commonlyadapted not only to the case in which the spatial light modulator andthe light sensing device are laminated and integrated in the verticaldirection, but also, to the case in which the spatial light modulatorand the light sensing device are abutted on each other without beingsuperposed for each pixel.

Next, the structure of the modulator/light sensing device, in which theSLM using the reflection type light interference light modulator in thepresent embodiment and the CMOS sensor, which is the light sensingdevice, are vertically integrated, that is, laminated, will bedescribed. FIG. 17 shows a cross section structure of the maincomponents of such a modulator/light sensing device. Here, the area fortwo pixel portions is shown, and described is an example using the CMOSsensor capable of reading at a high speed as the light sensing device.The type of the light sensing device is not particularly limited, and aCCD and other optical sensors may be used. Incidentally, since anoptical image pattern may be detected in the area only of theinformation beam at the reproducing time, the light sensing device maybe formed in the information beam area only in the SLM.

The surface of a single crystal silicon (Si) substrate 51 is formed witha photodiode 52 and is also provided with a gate electrode 53 of thetransfer switch of the CMOS sensor. To cover the entire surface of thesubstrate, an interlayer insulation film 60 is provided, and inside thisinterlay insulation film 60, a wiring 54 of the CMOS sensor, a wiring ofthe SLM, and a light shielding film 56 are provided. The light shieldingfilm 56 is for the purpose of the incident beam not to reach the lowertransistor area. Close to the most upper surface of the interlayerinsulation film 60, a reflection electrode 57 is provided. The wiring 54is connected to the source/drain electrode of the transfer switchthrough a contact hole, and the wiring 55 is connected to the reflectionelectrode 57 through the contact hole. At a position, which is thesurface of the interlayer insulation film 60 and equivalent to theperipheral edge portion of the reflection electrode 57, a columnarinsulation film 61 is provided, and, as if being supported by thisinsulation film 61, a semi-transparent film 58 is provided. Between thesemi-transparent film 58 and the reflection electrode 57, a space (airgap) 62 is provided. Within the surface of the semi-transparent film 58,the entire surface of the surface, which does not face with the air 62,is formed with a protection film 59. In this figure, a LOCOS oxide filmfor interpixel insulation, and the like, other transistors and wiringsof the CMOS sensor, and the pixel switches and wirings of the SLM areomitted.

In this modulator/light sensing device, interference is allowed to begenerated for the incident beam between the reflection electrode (firstinterference mirror) 57 and the semi-transparent film (secondinterference mirror) 58, and the distance of a space (for example, air)62 therebetween is changed, so that reflectance and transmittance arechanged. In this configuration, the SLM using the reflection type lightinterference light modulator and the CMOS sensor, which is the lightsensing device, are vertically integrated. Hence, when the lightentering the CMOS sensor, which is the light sensing device, is read, atransmission mode is used, and therefore, both of the interferencemirrors (that is, the semi-transparent film 68 and the reflectionelectrode 57) are required to be semi-transparent. However, in the caseof a horizontal arrangement, since there is no need to use thetransmission mode in the interference structure portion 4, thereflection electrode 57 need not be semi-transparent. When thereflection electrode 57 is not semi-transparent, it is preferable to usea material having a high reflectance as the reflection electrode 57,and, for example, a metal film, such as Al, AlSi, AlCu, Ti, Ta, W, Ag,Pt, Ru, Ni, Au, TiN, or a compound film of these metals, can be used.However, the materials of the reflection electrode are not limited tothose shown here. The columnar insulation film 61, arranged between thereflection electrode 57 and the semi-transparent film 58, for example,is formed by a silicon nitride film, and the protection film 59 of thesemi-transparent film 58, for example, is formed by a silicon oxidefilm. Incidentally, the columnar insulation film 61, the interlayerinsulation film 60, and the protection film 59, can be used without anyparticular limitation, provided that they are electrically insulatedmaterials, and moreover, they may be configured by different materialsor the same materials.

Next, the operation of this modulator/light sensing device as theinterference structure portion will be described. First, thesemi-transparent film 58 composed of Ti, for example, is given a grandpotential of 0V. By the above-described active matrix operation, thereflection electrode 57 is given a voltage corresponding to the signal,and a potential difference is generated between the reflection electrode57 and the semi-transparent film 58, and by a Coulomb force generated bythis potential difference, the air gap is changed. Assuming that thelight is incident on the illustrated upper side, a certain ratio portionof this incident beam is reflected by the surface of thesemi-transparent film 58, and the remaining portion transmits thesemi-transparent film 58, to be reflected by the reflection electrode57, and transmits the semi-transparent film 58, to be outputted outside.At this time, the component reflected on the surface of thesemi-transparent film 58 and the component reflected by the reflectionelectrode 57 interfere with each other, and the intensity of thereflection light, as a whole, is changed according to the potentialdifference between both of the components. The potential difference isdecided by an optical path difference, and the optical path differenceis two times the size of the air gap, and therefore, by changing the airgroup according to the signal voltage, the intensity of the reflectionlight (reflection light as a whole), as the interference structureportion, can be controlled.

FIG. 18 is a graph representing a wavelength change of the reflectanceat the time of 170 nm and 10 nm in an air gap, when the interferencestructure is provided, is configured in such a manner. Here, as theprotection film 59, SiO₂ of 10 nm in thickness is used, and as thesemi-transparent film 58, Ti of 5 nm in thickness, Si₃N₄ of 20 nm inthickness laminated in this order are used, and as the reflectionelectrode 57, Ti of 15 nm in thickness having SiO₂ film of 10 nm inthickness on the surface is used. As shown in FIG. 18, in the light of550 nm in wavelength, the reflectance at the time of 170 nm in air gapis 52.5% and the reflectance at the time of 10 nm is 1.2%. When the airgap is changed from 10 nm to 170 nm by the voltage of the signal givento the reflection electrode 57, it is clear that the reflectance issharply changed accompanied with that change. The interference action isdesignable depending on the wavelength, the semi-transparent filmmaterial, and the air gap, respectively. Consequently, it is importantfor the interference structure portion to have a necessary structure inview of the characteristics such as physical strength, a contrast ratio,and the like.

In the case of the read mode, in the pixel where at least theinformation beam enters, it is necessary that the transmittance is keptconstant with the state of the light interference kept in the samestate. Hence, FIG. 19 shows a wavelength change for the transmittance inthe case in which the air gap is taken as 100 nm, in thismodulator/light sensing device. In this case, though the transmittanceis 23.0% and is relatively low, it is important that it is constant, andthe absolute value of the transmittance is not so important. By keepingthe transmittance constant, it is possible to discriminate the intensityof the reproduced beam by the CMOS sensor, and to identify whether it isa white pixel or a black pixel.

Next, the fabricating method of the modulator/light sensing device, inwhich the spatial light modulator (SLM) composed of such a reflectiontype light interference modulator and the light sensing device, which isthe CMOS sensor, are integrated, will be described.

By using a silicon (Si) semiconductor substrate, a CMOS sensor is formedon this semiconductor substrate by a known method. As a specific formingmethod, any arbitrary method can be used. At the same time, anyarbitrary method can be used. At the same time, a write transistor(pixel switches 3, 3 a, . . . in FIG. 4) of the SLM is formed by an nMOStransistor. After that, an interlayer insulation film is formed, andeach wiring is formed, and moreover, a reflection type lightinterference modulator is formed. One example of a specific fabricatingprocedure is as follows.

The n-type single crystal silicon semiconductor substrate is thermallyoxidized locally, thereby forming a LOCOS (Local Oxidation of silicon)oxidized film. Then, with the LOCOS oxidized film as a mask, ions areimplanted with a dose amount of approximately 10¹¹ cm² of Boron (B),thereby forming a p type well, which a p type impurity area. Thissubstrate is thermally oxidized again, thereby forming a gate oxidizedfilm of 60 nm in thickness.

Next, a gate electrode 53 composed of an n type poly silicon withphosphorus (P) doped approximately at 10²⁰ cm³ is formed, and afterthat, the entire surface of the substrate is ion implanted with a doseamount of approximately 10¹³ cm² of phosphorus, thereby forming an ntype decreased level drain, which is an n type impurity area ofapproximately 10¹⁸ cm³ of the impurity concentration. Subsequently, witha patterned photo register as a mask, phosphorus is ion implanted with adose amount of approximately at 10¹⁵ cm², thereby forming a source/drainarea of the impurity concentration approximately at 10²⁰ cm³ and formingan pMOS transistor. Similarly, a pMOS transistor is formed.

The CMOS sensor is fabricated by a known technique. The transistorconfigured by the CMOS sensor can be formed at the same time with theforming process of the above-described transistor, and moreover, theprocess of the photo diode only may be added.

After that, the interlayer insulation film 60 is formed at the entiresurface of the substrate. For the interlayer insulation film a PSG(Phospho-Silicate Glass) film, an NSG (Nondope Silicate Glass)/BPSG(Boro-Phospho-Silicate Glass) film or a CVD (chemical vapor growth)film, and the like, by TEOS (Tetra ethoxy silane) can be used, and isnot particularly limited.

Next, a contact hole is patterned directly above the source/drain area,and an aluminum (Al) layer is deposited by spattering, and the like, andis patterned, thereby forming a wiring 54 of the backing. To improveohmic contact characteristics with this lower wiring layer 334 and thesource/drain area, it is desirable to form a barrier metal, such asTi/TiN, and the like, between the wiring 54 and the source/drain area.After that, the interlayer insulation film is formed, and moreover, bythe metallic film, the light shielding film 56 is formed. For the lightshielding film 56, for example, a metal film such as Ti, TiN, Al, Ag ora laminated film of those metals can be used, and are not particularlylimited.

After that, Ti is laminated approximately 15 nm in thickness by thesputtering method, and the like, and is patterned, thereby forming thereflection electrode 57. Then, as a protection film of the reflectingelectrode 57, a silicon oxide film of 15 nm in thickness is provided bya CVD method.

Next, a silicon nitride film is formed by a plasma CVD method, and acolumnar insulation film 61 is formed by etching after patterning. Afterthat, it is coated with a resist and flattened, and after that, it isflattened, so that the columnar insulation film 61 of approximately 180nm in height remains uniformly. Next, by a sputtering method of lowtemperatures, Si₃N₄: thickness of 20 nm, SiO₂: thickness of 10 nm,Si₃N₄: thickness of 20 nm, and Ti: thickness of 5 nm are formed inorder, and moreover, a silicon oxide film which becomes a protectionfilm 59 is laminated 10 nm in thickness. After patterning, a siliconnitride film, a silicon oxide film and a Ti layer are etched by dry orwet etching, and after that, the resist is removed by the wet etching.By this process, a semi-transparent film 58 and a protection film 59 areformed. After that, the electrode is extracted by wire bonding, therebyfinishing the reflection type light interference modulator.

Here, while an example of shifting a start position of the shiftregister has been shown in the present embodiment, the present inventionis not limited to this. Although the display position is similarlyshifted to the SLM, a start position of the shift register is notshifted, but the display position of [1 (white)] may be shifted. Thatis, though the entire effective pixel shows [1 (white)] or [0 (black)],by simply shifting the display position of [1 (white)], the entirepattern is displayed in a shifted manner, and becomes the same as apattern displayed by shifting the start position of the shift register.

Second Embodiment

In the present invention, as a correction method of the shift of anincident beam to a spatial light modulator, as described above, there isa method of physically moving the spatial light modulator itselfaccording to the shift amount in addition to the method of changing astart position of the shift register, and electrically correcting adisplay position at the spatial light modulator. FIG. 20 is a viewexplaining a shift correction by physical movement.

In FIG. 20, in the surface of the spatial light modulator, an actualincident beam 303 is shifted from a designed incident beam 301. Directlybelow the spatial light modulator, a light sensing device area of a CMOSsensor is provided, and each light receiving pixel shall be shown byreference numeral 302. Further, a point that serves as a reference forthe operations of a horizontal shift register and a vertical shiftregister is an original 310. In the present embodiment, for such ashift, as shown in FIG. 20, the shift of the actual incident beam 303from the designed incident beam 301 is corrected by shifting thephysical position of the spatial light modulator. In FIG. 20B, anoutline 312 shown by a broken line shows the initial position of thespatial light modulator, and an outline 313 shown by a solid line is aposition of the spatial light modulator after correcting the position inan XY direction. As described above, the spatial light modulator ismounted on a precision XY stage, and by adjusting the positions in the Xdirection and the Y direction of the XY stage according to the detectedshift amount, that is, by feeding back the detected shift amount to theXY stage, a correction can be made, so that the incident beam isirradiated on the display position of an original modulation signal asthe spatial light modulator.

Third Embodiment

In the above-described first embodiment, while the modulator/lightsensing device 108 has been configured by laminating the spatial lightmodulator (SLM) an the light sensing device (CMOS sensor) on the surfaceof the silicon semiconductor substrate in a vertical direction, themodulator/light sensing device used in the present invention is notlimited to this. In the modulator/light sensing device 108, the spatiallight modulator and the light sensing device may be arranged in ahorizontal posture for each pixel. FIG. 21 shows the modulator/lightsensing device 108 in which the SLM and the light sensing device arearranged in such a horizontal posture.

The modulator/light sensing device 108 shown in FIG. 8 comprises an SLMelement area 64 having the SLM composed of a reflection type lightinterference modulator and a CMOS sensor area 65 having a CMOS lightsensing device for each pixel. The SLM element area 64 and the CMOSsensor area 65 for each pixel are provided in the same silicon substrate51, and are arranged mutually adjacent.

The fabricating process of the modulator/light sensing device, as shownin FIG. 8, is basically the same as the fabricating process of themodulator/light sensing device arranged in a vertical posture shown inthe first embodiment. That is, while the SLM element area 64 is notprovided with a photodiode, but it is formed with an interferencestructure composed of a reflection electrode 57 and a semi-transparentfilm 58. On the other hand, the CMOS sensor area 65 is not formed withthe interference structure, but it is formed with a photodiode 52.Although not shown, in this structure. when a micro lens is arranged onthe CMOS sensor area 65, an effective open ratio is increased.

In the case of such a modulator/light sensing device arranged in such ahorizontal posture, in the reflection type light interference modulatorconfiguring the SLM, there is no need for a transmission mode forguiding the light to the light sensing device, and therefore, it ispossible to use a relatively thick film composed of aluminum (Al), andthe like, as the reflection electrode 57.

FIG. 22 is a graph representing the wavelength change of reflectance atthe time of 180 nm and 10 nm in the air gap when the interferencestructure portion is configured in this manner. Here, as the protectionfilm 59, SiO₂ of 10 nm in thickness is used, and as the semi-transparentfilm 58, Ti of 5 nm in thickness, Si₃N₄ of 20 nm in thickness, SiO₂ of10 nm in thickness, and Si₃N₄ of 20 nm in thickness laminated in thisorder were used, and as the reflection electrode 57, AlSi of 15 nm inthickness having an SiO₂ film of 10 nm in thickness on the surface wasused. As shown in FIG. 6, in the light having a wavelength of 550 nm,the reflectance at the time of 180 nm in the air gap is 93.0%, and thereflectance at the time of 10 nm is 0.6%. By the voltage of the signalgiven to the reflectance electrode 57, when the air gap is changed from10 nm to 180 nm, it is clear that the reflectance is sharply changed,accompanied with this change. This interference action is designabledepending on the wavelength, the semi-transparent film material, and theair gap, respectively, and consequently, it is important for theinterference structure portion to have a necessary structure in view ofthe characteristics such as physical strength, a contrast ratio, and thelike.

Further, in the present invention, as the spatial light modulatorconfiguring the modulator/light sensing device, a reflection type liquidcrystal on silicon (LCOS) can be used. The modulator shown in FIG. 23uses the LCOS as the spatial light modulator, and arranges thereflection type liquid crystal on silicon (LCOS) and the CMOS (sensor)in a vertical posture in the modulator/light sensing device.

The surface of a silicon substrate 51 is provided with a photodiode 52and a gate electrode 53 of a transfer switch, and at the same time, aninterlayer insulation film 60 is provided on its top. Wirings 54 and 55,and a light shielding film 56 being provided in the interlayerinsulating film 60, is the same as the modulator/light sensing deviceshown in FIG. 5. In the modulator/light sensing device shown in FIG. 10,close to the surface of the interlayer insulation film 60, a pixelelectrode 66 for each pixel is provided. Opposing the interlayerinsulation film 60, a glass plate 70 is arranged, and between theinterlayer insulation film 60 and the glass plate 70, a liquid crystal68 is sealed. The surface of the liquid crystal 68 side of the glassplate 70 is formed with an ITO (indium/tin oxide) film 69, which becomesa common electrode, and the surface of the ITO film 69 and the surfaceof the interlayer insulation film 60 are formed with an orientation film67. Here, as the liquid crystal 68, a vertical liquid crystal is used,and as the orientation film 67, a rhomble deposition SiO₂ film is used.A pixel electrode 66 is, for example, provided as a semi-transparentfilm having a reflectance of 50%. Incidentally, in this modulator/lightsensing device, a composition and a thickness of the liquid crystal 68are designed such that when an incident beam (wavelength: A) passesthrough the liquid crystal 68, and is reflected by the pixel electrode66, and passes through the liquid crystal 68 again, a phase shift of λ/2is generated.

In such a modulator/light sensing device, in the case of the [1]display, the voltage is applied between the pixel electrode 66 and thecommon electrode 69, and an electrical field is applied to the liquidcrystal 68, so that a liquid crystal molecule falls down. On the otherhand, in the case of the [0] display, the electrical field is notapplied, so that the liquid crystal molecule vertically stands up. Ifsuch a reflection type liquid crystal on silicon is used as the spatiallight modulator, in the optical system shown in the first embodiment,when the light turned into a linear polarized light of an S polarizationby the PBS (polarized beam splitter) 104, before entering, is allowed toenter the modulator/light sensing device 108, the polarized direction isnot changed, but the light is reflected by the pixel electrode with anintensity of 50% in the case of the [0] display. In this case, thoughthe reflected light enters the PBS 104 again, since the polarization isnot changed, it is reflected by the PBS 104, and the light does notreach the recording medium (hologram) 118. On the other hand, in thecase of the [1] display, though a reflectance by the pixel electrode 66is 50%, since the composition and thickness of the liquid crystal areset as described above, the reflected light beam becomes a linearpolarized light with a plane of polarization rotated 90°. Consequently,this reflected light enters and transmits the PBS 104 by P polarization,and is oriented to the recording medium 118. Although the intensity ofthe light becomes 50% even in the case of [1], it is still of sufficientstrength to discriminate [1] and [0].

When reading the information recorded in the recording medium 118, sincethe liquid crystal 68 may only allow the reproduced beam to transmit inthe information light area, a polarized state of the liquid crystal 68may be in any state, and it does not matter if the liquid crystal 68 isin whatever state.

In the present invention, similar to the case of the reflection typelight interference modulator, even when the reflection type liquidcrystal on silicon (LCOS) is used as the spatial light modulator in themodulator/light sensing device, the spatial light modulator and thelight sensing device for each pixel can be arranged in a horizontalposture on the silicon substrate. FIG. 24 shows the modulator/lightsensing device arranged in such a horizontal posture.

The modulator/light sensing device shown in FIG. 24 comprises the SLMelement area 64 having the SLM composed of the reflection type liquidcrystal on silicon and the CMOS sensor area 65 having the CMOS lightsensing device for each pixel. The SLM element area 64 and the CMOSsensor area 65 for each pixel are provided on the same silicon substrate51 and are arranged mutually adjacent. The operation as the spatiallight modulator of this modulator/light sensing device is the same asthe case of the above-described arrangement in the vertical posture, inthe case of recording the information and in the case of reproducing theinformation.

While the present invention has been described with reference to theexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

1. An optical information recording and reproducing apparatus forrecording information on a recording medium by forming interferencefringes generated by interference between an information beam and areference beam on the recording medium, and reproducing the informationby irradiating the recording medium with the reference beam, in whichthe interference fringes are formed, said apparatus comprising: aspatial light modulator for spatially modulating at least a portion of alight beam emitted from a light source into the information beam; alight sensing device that reads the information beam extracted from therecording medium by the reference beam irradiated on the recordingmedium; a shift amount detector that detects a shift of an irradiatingposition of the light beam entering said spatial light modulator; and acorrection device that corrects a positional shift between a position ofan area for modulating the information beam and a position of the lightbeam in said spatial light modulator, based on a positional shift amountdetected by said shift amount detector, wherein said spatial lightmodulator comprises a plurality of pixels, and is configured such thateffective pixels are allowed to function as pixels for the referencebeam and pixels for the information beam, and the area of the effectivepixels of said spatial light modulator is divided into the area for thereference beam and the area for the information beam, according to aposition based on the detected positional shift amount.
 2. The opticalinformation recording and reproducing apparatus according to claim 1,further comprising a shift register for writing a signal for each pixelin the effective pixel area, such that the positional shift is correctedby correcting a start position in said shift register.
 3. An opticalinformation recording and reproducing apparatus for recordinginformation on a recording medium by forming interference fringesgenerated by interference between an information beam and a referencebeam on the recording medium, and reproducing the information byirradiating the recording medium with the reference beam, in which theinterference fringes are formed, said apparatus comprising: a spatiallight modulator for spatially modulating at least a portion of a lightbeam emitted from a light source into the information beam; a lightsensing device that reads the information beam extracted from therecording medium by the reference beam irradiated on the recordingmedium; a shift amount detector that detects a shift of the irradiatingposition of the light beam entering said spatial light modulator; and acorrection device that corrects a positional shift between a position ofan area for modulating the information beam and a position of the lightbeam in said spatial light modulator, based on a positional shift amountdetected by said shift amount detector, wherein said spatial lightmodulator and said light sensing device are integrally formed on thesame substrate, and said spatial light modulator and said light sensingdevice are laminated so that said spatial light modulator is arranged atthe light source side, and a pixel pitch in said spatial light modulatorand a pixel pitch in said light sensing device match, so that the pixelin said spatial light modulator and the pixel corresponding to saidlight sensing device are arranged along an optical axis of the lightincident from the light source, and at least a portion of the lightincident on said spatial light modulator transmits toward said lightsensing device.
 4. An optical information recording and reproducingapparatus for recording information on a recording medium by forminginterference fringes generated by interference between an informationbeam and a reference beam on the recording medium, and reproducing theinformation by irradiating the recording medium with the reference beam,in which the interference fringes are formed, said apparatus comprising:a spatial light modulator for spatially modulating at least a portion ofa light beam emitted from a light source into the information beam; alight sensing device that reads the information beam extracted from therecording medium by the reference beam irradiated on the recordingmedium; a shift amount detector that detects a shift of the irradiatingposition of the light beam entering said spatial light modulator; and acorrection device that corrects a positional shift between a position ofan area for modulating the information beam and a position of the lightbeam in said spatial light modulator, based on a positional shift amountdetected by said shift amount detector, wherein said spatial lightmodulator and said light sensing device are integrally formed on thesame substrate, and said spatial light modulator and said light sensingdevice are arranged mutually adjacent, so that a pixel in said spatiallight modulator and a corresponding pixel in said light sensing deviceare not superposed along the optical axis of the light incident from thelight source.
 5. An optical information recording and reproducingapparatus for recording information on a recording medium by forminginterference fringes generated by interference between an informationbeam and a reference beam on the recording medium, and reproducing theinformation by irradiating the recording medium with the reference beam,in which the interference fringes are formed, said apparatus comprising:a spatial light modulator for spatially modulating at least a portion ofa light beam emitted from a light source into the information beam; alight sensing device that reads the information beam extracted from therecording medium by the reference beam irradiated on the recordingmedium; a shift amount detector that detects a shift of the irradiatingposition of the light beam entering said spatial shift modulator; and acorrection device that corrects a positional shift between a position ofan area for modulating the information beam and a position of the lightbeam in said spatial light modulator, based on a positional shift amountdetected by said shift amount detector, wherein said spatial lightmodulator comprises a plurality of modulators changing in the intensityof the reflection light according to a modulation signal, and saidspatial light modulator is a pixel comprising a reflection electrodereflecting the light from the light source and a semi-transparent filmarranged at the light source side than the reflection electrode throughan air gap, and a semi-transparent film showing a semi-transparencyproperty for the light from the light source, wherein a reflectance ofthe light from the light source is changed by controlling a spacebetween the reflection electrode and the semi-transparent film.
 6. Anoptical information recording apparatus for recording information on arecording medium by forming interference fringes generated byinterference between an information beam and a reference beam on therecording medium, said apparatus comprising: a spatial light modulatorfor spatially modulating at least a portion of a light beam emitted froma light source into the information beam; an optical system that allowsthe reference beam from the light source and the information beam fromsaid spatial light modulator to interfere at a predetermined depth ofthe recording medium; a shift amount detector that detects a shift ofthe irradiating position of a light beam entering said spatial lightmodulator; and a correction device that corrects a shift between aposition of an area for modulating the information beam and a positionof the light beam in said spatial light modulator, based on a positionalshift amount detected by said shift amount detector, wherein saidspatial light modulator comprises a plurality of pixels, and isconfigured such that effective pixels are allowed to function as pixelsfor the reference beam and pixels for the information beam, and the areaof the effective pixels of said spatial light modulator is divided intothe area for the reference beam and the area for the information beam,according to a position based on the detected positional shift amount.7. The optical information recording and reproducing apparatus accordingto claim 6, further comprising: a second optical system that introducesthe reference beam into the predetermined depth of the recording medium,reproduces the information beam from the interference fringes, andextracts the reproduced information beam; and a third optical systemthat guides the extracted information beam to the light sensing device.8. The optical information recording and reproducing apparatus accordingto claim 6, wherein said correction device corrects the detectedpositional shift amount by performing feedback.
 9. The opticalinformation recording and reproducing apparatus according to claim 6,further comprising a shift register for writing a signal for each pixelin the effective pixel area, such that the positional shift is correctedby correcting a start position in said shift register.
 10. The opticalinformation recording and reproducing apparatus according to claim 6,wherein said correction device comprises a device for mechanicallymoving a position of said spatial light modulator relative to the lightbeam.
 11. The optical information recording and reproducing apparatusaccording to claim 6, wherein said modulator is a reflection type liquidcrystal on silicon.
 12. An optical information recording apparatus forrecording information on a recording medium by forming interferencefringes generated by interference between an information beam and areference beam on the recording medium, said apparatus comprising: aspatial light modulator for spatially modulating at least a portion of alight beam emitted from a light source into the information beam; alight sensing device that reads the information beam extracted from therecording medium by the reference beam irradiated on the recordingmedium; an optical system that allows the reference beam from the lightsource and the information beam from said spatial light modulator tointerfere at a predetermined depth of the recording medium; a shiftamount detector that detects a shift of the irradiating position of thelight beam entering said spatial light modulator; and a correctiondevice that corrects a shift between a position of an area formodulating the information beam and a position of the light beam in saidspatial light modulator, based on a positional shift amount detected bysaid shift amount detector, wherein said spatial light modulator andsaid light sensing device are integrally formed on the same substrate,and said spatial light modulator and said light sensing device arelaminated so that said spatial light modulator is arranged at the lightsource side, and a pixel pitch in said spatial light modulator and apixel pitch in said light sensing device match, so that the pixel insaid spatial light modulator and the pixel corresponding to the lightsensing device are arranged along an optical axis of the light incidentfrom the light source, and at least a portion of the light incident onsaid spatial light modulator transmits toward the light sensing device.13. The optical information recording and reproducing apparatusaccording to claim 12, further comprising: a second optical system thatintroduces the reference beam into the predetermined depth of therecording medium, reproduces the information beam from the interferencefringes, and extracts the reproduced information beam; and a thirdoptical system that guides the extracted information beam to the lightsensing device.
 14. The optical information recording and reproducingapparatus according to claim 12, wherein said correction device correctsthe detected positional shift amount by performing feedback.
 15. Theoptical information recording and reproducing apparatus according toclaims 12, wherein said correction device comprises a device formechanically moving a position of said spatial light modulator relativeto the light beam.
 16. The optical information recording and reproducingapparatus according to claim 12, wherein said modulator is a reflectiontype liquid crystal on silicon.
 17. An optical information recordingapparatus for recording information on a recording medium by forminginterference fringes generated by interference between an informationbeam and a reference beam on the recording medium, said apparatuscomprising: a spatial light modulator for spatially modulating at leasta portion of a light beam emitted from a light source into theinformation beam; a light sensing device that reads the information beamextracted from the recording medium by the reference beam irradiated onthe recording medium; an optical system that allows the reference beamfrom the light source and the information beam from said spatial lightmodulator to interfere at a predetermined depth of the recording medium;a shift amount detector that detects a shift of an irradiating positionof the light beam entering said spatial light modulator; and acorrection device that corrects a shift between a position of an areafor modulating the information beam and a position of the light beam insaid spatial light modulator, based on a positional shift amountdetected by said shift amount detector, wherein said spatial lightmodulator and said light sensing device are integrally formed on thesame substrate, and said spatial light modulator and said light sensingdevice are arranged mutually adjacent, so that a pixel in said spatiallight modulator and a corresponding pixel in said light sensing deviceare not superposed along the optical axis of the light incident from thelight source.
 18. The optical information recording and reproducingapparatus according to claim 17, further comprising: a second opticalsystem that introduces the reference beam into the predetermined depthof the recording medium, reproduces the information beam from theinterference fringes, and extracts the reproduced information beam; anda third optical system that guides the extracted information beam to thelight sensing device.
 19. The optical information recording andreproducing apparatus according to claim 17, wherein said correctiondevice corrects the detected positional shift amount by performingfeedback.
 20. The optical information recording and reproducingapparatus according to claims 17, wherein said correction devicecomprises a device for mechanically moving a position of said spatiallight modulator relative to the light beam.
 21. The optical informationrecording and reproducing apparatus according to claim 17, wherein saidlight modulator is a reflection type liquid crystal on silicon.
 22. Anoptical information recording apparatus for recording information on arecording medium by interference fringes generated by interferencebetween an information beam and a reference beam on the recordingmedium, said apparatus comprising: a spatial light modulator forspatially modulating at least a portion of a light beam emitted from alight source into the information beam; an optical system that allowsthe reference beam from the light source and the information beam fromsaid spatial light modulator to interfere at a predetermined depth ofthe recording medium; a shift amount detector that detects a shift ofthe irradiating position of a light beam entering said spatial lightmodulator; and a correction device that corrects a shift between aposition of an area for modulating the information beam and a positionof the light beam in said spatial light modulator, based on a positionalshift amount detected by said shift amount detector, wherein saidspatial light modulator comprises a plurality of modulators changing inthe intensity of the reflection light according to a modulation signal,and said spatial light modulator is a pixel comprising a reflectionelectrode reflecting the light from the light source and asemi-transparent film arranged at the light source side than thereflection electrode through an air gap, and a semi-transparent filmshowing a semi-transparency property for the light from the lightsource, wherein a reflectance of the light from the light source ischanged by controlling a space between the reflection electrode and thesemi-transparent film.
 23. The optical information recording andreproducing apparatus according to claim 22, further comprising: asecond optical system that introduces the reference beam into thepredetermined depth of the recording medium, reproduces the informationbeam from the interference fringes, and extracts the reproducedinformation beam; and a third optical system that guides the extractedinformation beam to the light sensing device.
 24. The opticalinformation recording and reproducing apparatus according to claim 22,wherein said correction device corrects the detected positional shiftamount by performing feedback.
 25. The optical information recording andreproducing apparatus according to claims 22, wherein said correctiondevice comprises a device for mechanically moving a position of saidspatial light modulator relative to the light beam.
 26. The opticalinformation recording and reproducing apparatus according to claim 22,wherein said spatial light modulator is a reflection type liquid crystalon silicon.